1. Field of the Invention
The invention is in the field of medical technology and relates to a device of which at least a part is suitable for being implanted in a human or animal body and which is equipped for material or signal delivery or acquisition within the body. The invention also concerns methods for implanting the named implantable devices or implantable device parts.
2. Description of Related Art
Devices for material delivery within a body are in particular drug delivery devices (delivering therapeutically or prophylactically active molecules or particles into tissue) and infusion devices but may also serve for delivering other materials such as e.g. contrast agents or fluorescent molecules, viable cells (e.g. for differentiation and integration in the tissue or for production of a desired protein) or subatomic particles (particle radiation) within the body. Devices for material acquisition within a body are e.g. catheters or hollow needles for removing tissue components or body fluids e.g. for therapeutic or diagnostic purposes. Devices for signal delivery within a body serve e.g. for stimulating tissue, for activating deposited chemicals, or for activating other implanted devices such as e.g. drug delivery devices, wherein the signals to be delivered within the body may be e.g. electric, mechanic, acoustic or optic signals. Devices for signal acquisition within a body serve e.g. diagnostic purposes, wherein the signal acquisition may comprise e.g. acquisition of signals transmitted into tissue, measuring a local body temperature, pressure, or chemistry, or sensing the state of another implanted device such as e.g. a drug delivery device.
Devices for material or signal delivery or acquisition within a body may also be equipped for combinations of the above named functions such as e.g. a combination of signal delivery and signal acquisition for diagnostic (e.g. scanning) purposes or a combination of a drug delivery function combined with a signal acquisition function for detecting a need for delivery in the concerned tissue and a signal delivery function for activation of the drug delivery function. In many cases the named devices comprise electronic or microelectric and/or micromechanic elements. The devices may be fully implanted or they may comprise parts to be implanted and parts which are situated outside of the body, wherein the implanted parts are physically or functionally connected or connectable to the non-implanted parts, and wherein for such cases the invention concerns the implanted device part only. Examples for such only partly implanted devices are e.g. devices comprising an implanted catheter and non-implanted reservoir and drive means, devices comprising an implanted sensor and a non-implanted device part for registration of the sensor readings, or systems comprising an implanted identification chip (RFID) and a non implanted reading device.
The term “device for implantation in a human or animal body for material or signal delivery or acquisition” as used in connection with the present invention is understood to comprise all the above named groups and examples of implantable devices or implantable device parts and all devices and device parts which one skilled in the art will subsume under the named groups.
Implantable drug delivery devices are well known in today's medicine. Such drug delivery devices are usually designed for sustained and/or delayed release of the drug, wherein the delivery process may be controlled by chemical characteristics of the device (e.g. biological resorption of device components enclosing the drug), by control means, which are e.g. integrated in the device to activate the delivery either fully automatically or through signals or actions initiated from outside of the body.
The known implantable drug delivery devices as well as other known implantable devices for material or signal delivery or acquisition such as implantable devices comprising electronic or microelectric and/or micromechanic elements (e.g. RFID-chips, sensors, cardiac pulse generators, electric or mechanic elements for activating delivery devices) are implanted to be either “floating” (e.g. subcutaneously implanted) or to be fixed in a specific body location (e.g. by being tied to soft tissue with suture or wire or by being fixed to hard tissue with the aid of a bone anchor with or without suture). Floating implantation is in particular known for RFID-chips (e.g. for identification of animals) and for drug delivery devices. Fixed implantation is more involved but in many cases advantageous as it prevents migration of the device in the body. Regarding drug delivery, fixed implantation is particularly advantageous if the drug is to be administered locally, wherein the fixation location is chosen to coincide as closely as possible with the location of the desired administration.
Drug delivery devices suitable for fixed implantation in bone tissue are e.g. described in the publication U.S. Pat. No. 6,936,270. The described devices comprise an e.g. metallic osteosynthesis element such as a bone screw, bone nail or bone staple to be at least partly embedded in the bone tissue. The drug and possibly a suitable drug carrier is contained in the screw or nail head or in a container fixed to the middle section of the staple and the head or container is designed for delivery of the drug to tissue or body fluid situated adjacent to the bone in which the device is anchored. The devices are said to be particularly suited for implantation within a synovial joint and for delivering a drug into the synovial fluid of the joint.
Also known (e.g. WO 2005/053795) are drug delivery devices in the form of cannulated bone screws comprising openings connecting the axial screw channel with the threaded screw surface and containing the drug to be delivered in the channel, the drug being delivered through the openings to the bone tissue in which the screw is embedded.
Implantable drug delivery devices comprising an osteosynthesis element (e.g. bone screws or plates) being made of a biodegradable material are described e.g. in the publication U.S. Pat. No. 6,214,008. According to this publication, the drug (e.g. growth factor GF or bone morphogenic protein BMP) is integrated in the biodegradable material of the osteosynthesis element and is released with a rate directly dependent on the degradation rate of the biodegradable material. The devices are said to be particularly advantageous for delivering the drugs to bone defect locations, e.g. to a fractured bone tissue, for furthering bone repair.
For the above mentioned known drug delivery devices designed for fixed implantation in bone tissue, the fixation of the device is usually coupled with producing a bone defect, i.e. an opening in the bone tissue originating from a bone surface (accessible bone surface) and usually penetrating a cortical bone layer to reach into the cancellous bone tissue situated beneath the cortical bone layer. This means that the opening, even if it is only small, constitutes a non-natural passage from a first body region (on the accessible side of e.g. the cortical bone layer) to a second body region (on the non-accessible side of e.g. the cortical bone layer), wherein characteristics, functions and needs of the two body regions may differ considerably, and wherein, before the opening was provided, the two body regions were naturally and appropriately sealingly separated from each other by e.g. the cortical bone layer. It is known that bone screws, bone nails or bone staples implanted in such openings are not capable of mending the natural barrier function of the cortical bone layer completely. Chemicals and even bacteria will be able to pass through the impaired cortical bone layer along the device surface, in particular when an initial press fit has relaxed or, in the case of bioresorbable devices, when resorption has started. This means that the above shortly described known drug delivery devices, when fixed to or in bone not only constitute a possibly undesired impairment of a natural barrier function of the cortical bone layer but also are not able to fully limit delivery of the drug to one side of the cortical bone layer, even if they are designed specifically for such a purpose (delivery to accessible side of cortical layer according to U.S. Pat. No. 6,936,270 or delivery to non-accessible side of cortical layer according to WO 2005/053795 or U.S. Pat. No. 6,214,008).